基于全网冲突的自适应退避算法的研究

退避算法的设计对基于竞争的IEEE 802.11协议影响重大,而退避的前提取决于冲突的发生和正确判断。本文在DCF协议的基础上提出了一种基于全网冲突的自适应调整竞争窗口的新型退避算法(CWN-BEB),CWN-BEB算法通过统计全网冲突次数(即整个网络所有节点发生冲突的总次数),使全网冲突对节点透明,并引入一个新的变量全网冲突概率来自适应改变竞争窗口大小。此算法未引入额外开销,可以很好地与802.11 DCF协议兼容,实现复杂度低。仿真结果表明,在低负载情况下,CWN-BEB算法可以较好地向DCF协议收敛；在高负载情况下,CWN-BEB的时延和吞吐量等性能明显优于802.11 DCF协议。

Self-Adaptive Back-Off Algorithm Based onWhole Network Collisions

The design of backoff algorithm has an important impact on IEEE 802.11 protocol utilizing Distributed Coordination Function (DCF) as the commercial WLAN MAC access mechanism, and the precondition of backoff lies on whether the collision happened and distinguished correctly. In this paper, we propose a new Binary Exponential Backoff algorithm which is based on Collisions of the Whole Network(CWN-BEB).CWN-BEB adds up all the collisions happened in the network and makes it known to all the nodes, and then introduces a new variable (whole network probability) to self-adaptively change the value of contention window based on the collisions in the network. CWN-BEB can be easily implemented without any additional overheads and it is backward compatible with 802.11 DCF protocol. Finally, the simulation results demonstrate that when in low-duty situations, the performances of delay and throughput of CWN-BEB can well converge to 802.11 DCF protocol.in heavy-duty situations, the performances of delay and throughput of CWN-BEB are better than that of 802.11 DCF protocol.